Steam drive in an oil-bearing stratum adjacent a gas zone



Dec. 19, 1967 H. w. PARKER STEAM DRIVE IN AN OIL-BEARING STRATUMADJACENT A GAS ZONE Filed July 19, 1965 PRODUCT 26 STEAM INVENTOR ,7 ATQRNEKS United States Patent Ofi 3,358,759 Patented Dec. 19, 1967 ice3,358,759 STEAM DRIVE IN AN OIL-BEARING STRATUM ADJACENT A GAS ZONEHarry W. Parker, Bartlcsviile, kla., assignor to Phillips PetroleumCompany, a corporation of Delaware Filed July 19, 1965, Ser. No. 473,0598 Claims. (Cl. 166-11) ABSTRACT OF THE DISCLOSURE This invention relatesto a process for producing oil from an oil-bearing stratum lyingadjacent a gas zone, such as a gas cap, by fluid drive.

Recovery of oil by fluid drive, and particularly by steam injection, israpidly becoming a conventional technique in petroleum production. Inoil fields in which the oilbearing stratum lies adjacent a gas zone,there is a strong tendency for the steam or other injected fluid tobypass the major portion of the oil stratum between the injection andproduction wells and pass into the gas zone. Even in operation in whichthe steam is injected into the stratum near the bottom, there is aconsiderable tendency for the steam to rise and pass into the gas cap ashort distance from the injection well. Condensation of steam in the gascap or other gas zone gives up its heat to the unproductive zone andresults in tremendous waste of steam.

The instant invention is concerned with an improved process forproducing oil from an oil stratum lying adjacent a gas zone such as agas cap without substantial loss of injected steam or other fluid intothe gas zone.

Accordingly, the principal object of the invention is to provide aprocess for producing oil from an oil stratum lying adjacent a gas zone.Another object is to conserve steam or other injected fluid in theproduction of oil from such a stratum by fluid drive. A further objectis to provide a process for injecting a heating fluid such as steam deepinto a stratum from an injection well in this type of stratum whileconserving the injected fluid. Other objects of the invention willbecome apparent to one skilled in the art upon consideration of theaccompanying disclosure.

A broad aspect of the invention comprises fracturing an oil stratumlying adjacent a gas zone at a level remote from the gas zone thru aninjection well penetrating the stratum, injecting a driving fluid suchas steam into the fracture toward at least one offset production well soas to drive oil toward and into the production well(s), injecting anon-condensible gas thru the injection well into the gas zone so as toobstruct the passage of driving fluid into this zone, and recovering oilfrom the production well(s). In conjunction with the foregoing steps,the permeable walls of the fracture are at least partially plugged byinjecting an aqueous slurry of a particulate solid plugging agent, suchas clay, and the injection pressure is applied so as to extend thefracture deeper into the stratum. The extension of the fracture deeperinto the stratum is usually effected with fracturing fluid free ofplugging agent. After extending the fracture deeper into the stratum,the injection of steam or other driving fluid is re sumed so as todeliver the steam deeper in the stratum and extend the heated zone.

The injection of non-condensible gas into the gas zone may be effectedthru the stratum adjacent the gas zone or directly into the gas zone. Aconvenient method of injecting the driving fluid and the non-condensiblegas comprises injecting the steam into the fracture thru a tubing stringextending well into the stratum being produced and packing off theannulus around the tubing between the fracture and the level at whichthe non-condensible gas is injected. The non-condensible gas is theninjected thru the annulus into the surrounding formation above thepacker. The injection of the non-condensible gas may be commenced beforethe injection of steam, simultaneously therewith, or shortly after theinitiation of steam injection. It is also feasible to inject thenon-condensible gas continuously during steam injection or periodically(intermittently). The amount of gas injected into the gas cap dependsupon the extent of this zone and the well spacing.

Non-condensible gases suitable for use in the invention comprisenitrogen, air, helium, natural gas, or any normally gaseous hydrocarbon,CO or flue gas, etc. In fact, any non-condensible gas is operable andthe selection of this gas will be dictated by economics. Air is thepreferred gas in view of its availability and low cost.

When utilizing steam drive thru the fracture extending into the oilstratum, after an extended period of heating and driving oil toward thesurrounding production wells, it is advantageous to close in theproduction wells while continuing the injection of steam so as to buildup substantial stratum pressure, and thereafter opening the injectionwell to production so that the heated oil in the stratum, rendered morefluid by the heating, flows into the injection well from which it isproduced in conven tional manner as by pumping. It is preferred to allowa substantial soaking period such as a period of several days afterterminating steam injection and before opening the injection Well toproduction. After a substantial production period, steam injection isresumed and the production wells are opened to production so as tocontinue the healting and driving of more fluid oil into the productionwe s.

It is good practice to pack off the production wells around the tubingstring therein at an intermediate level of the stratum to assist indirecting the driving and heating fluid and the produced oil thru thestratum into the production wells. This in combination with theinjection of non-condensible gases prevents substantial loss of steam tothe gas zone.

The steam or other fluid drive of the invention may be effected thru aconventional ring-well pattern with a central injection well or in anin-line drive pattern from a line of injection wells to offset lines ofproduction Wells.

Fluids utilizable in the fluid drive include light liquid hydrocarbonsand mixtures thereof, air, CO or flue gas, etc. When utilizing air,ignition may be effected and the drive may principally comprise that ofin situ combustion wherein hot fluidized and cracked hydrocarbonstogether with combustion gas sweep thru the stratum. However, steam isthe preferred and most beneficial driving fluid to be used incombination with the fracturing and injection of non-condensible gas. Itis also feasible to inject air into the gas zone and to conduct an insitu combustion operation in the stratum along the area thereof boundingthe gas zone and driving the produced hydrocarbons into the productionwells.

A more complete understanding of the invention may be had by referenceto the accompanying schematic drawing which is an elevation through aformation penetrated by an injection well and a production well.

Referring to the drawing, an oil zone 10 lying below a gas cap 12 ispenetrated by an injection well 14 and 0 a production well 16. A tubingstring 18 extends into stratum 10 and a similar tubing string 20 extendsinto production well 16. Wells 14 and 16 are provided with casingstrings 22 and 24, respectively. Steam or other driving fluid isinjected into well 14 through line 26. Noncondensible gas is injectedinto the annulus of Well 14 through line 28. When well 14 is onproduction, after a heating and soaking period, oil is produced throughtubing 30 by conventional pumping means or gas lift. Apparatus isavailable for injecting steam through tubing string 18 without pullingthe pump (not shown) on the end of the tubing string. This type ofequipment is disclosed in US. application Ser. No. 372,553, filed June4, 1964, by W. B. Belknap, now US. Patent No. 3,312,281.

Packer 32 packs off the annulus between the tubing and casing in well 14and similar packer 54 positioned at an intermediate level in stratum 10packs oif the annulus in well 16.

Casing 22 is perforated in the gas cap area at 36 for injection ofnon-condensible gas. Casing 24 is not perforated in the gas cap zone soas to permit building up of pressure in this area. Casing 22 is alsoperforated at 38 for injection of fracturing fluid to form fracture 40and for the injection of steam or other driving fluid. The slurry ofplugging agent is also injected through the tubing and throughperforations 38 to line the walls of the fracture.

Perforations 42 in casing 24 below packer 34 provide for flow of oil andother fluids into production well 16 from which they are producedthrough tubing string 20 into production line 44.

Well 14 may represent a central well surrounded by any suitable numberof production wells 16 or it may represent a line of injection wells inbetween parallel lines of production wells 16.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing oil from an oil-bearing stratum lyingadjacent a gas-bearing zone which comprises the steps of:

(1) fracturing said stratum at a level remote from said zone through aninjection well therein;

(2) injecting steam into said fracture toward at least one oifsetproduction well so as to produce oil therein;

(3) injecting a non-condensible gas into said stratum adjacent said zoneso as to obstruct the passage of steam into said zone; and

(4) recovering oil from said at least one production well.

2. The process of claim 1 including the steps of:

(5) injecting an aqueous slurry of a particulate solid plugging agentinto said fracture so as to fracture deeper in said stratum; and

(6) thereafter injecting additional driving fluid into said stratumthrough said fracture.

3. The process of claim 1 wherein said gas-bearing zone is above saidstratum and said fracture is formed in a lower section of said stratum.

4. The process of claim 3 wherein steam is injected as the driving fluidthrough a tubing string extending into said stratum and the surroundingannulus is packed off at an upper level of said stratum.

5. The process of claim 1 wherein air is injected into said gas-bearingzone in step (3).

6. A process for producing oil from an oil-bearing stratum lying below agas cap which comprises the steps of:

(1) fracturing said stratum at a lower level therein through aninjection well penetrating said stratum so as to form a radiallyextending fracture around said well;

(2) injecting steam under substantial pressure into said fracturethrough a tubing string extending into said stratum so as to heat theoil in the stratum above and below the fracture and drive oil intosurrounding production wells;

(3) prior to injecting any substantial amount of steam in step (2),injecting a non-condensible gas into said gas cap so as to obstruct thepassage of steam into said gas cap and more effectively utilize the heatin said steam in producing oil;

(4) terminating the flow of steam and injecting an aqueous slurry ofclay into said fracture so as to at least partially plug the walls ofsaid fracture and extend same deeper into said stratum; and

(5) subsequent to step (4) again injecting steam into said fracture soas to heat oil deeper in said stratum and drive additional oil into saidproduction wells.

7. The process of claim 6 wherein the non-condensible gas in step (3) isintermittently injected during steam injection in steps (2) and (5).

8. The process of claim 6 wherein the production wells are shut-induring steam injection until substantial pressure is built up in saidstratum, thereafter steam injection is terminated, after a soakingperiod said injection well is opened to production and oil flowing intosame is produced, and steam injection is resumed with production throughsaid production wells.

References Cited UNITED STATES PATENTS 3,159,215 12/1964 Meldau et al.16611 X 3,167,121 1/1965 Sharp 166-11 3,259,186 7/1966 Dietz 166l 1STEPHEN J. NOVOSAD, Primary Examiner.

1. A PROCESS FOR PRODUCING OIL FROM AN OIL-BEARING STRATUM LYINGADJACENT A GAS-BEARING ZONE WHICH COMPRISES THE STEPS OF: (1) FRACTURINGSAID STRATUM AT A LEVEL REMOTE FROM SAID ZONE THROUGH AN INJECTION WELLTHEREIN; (2) INJECTING STEAM INTO SAID FRACTURE TOWARD AT LEAST ONEOFFSET PRODUCTION WELL SO AS TO PRODUCE OIL THEREIN; (3) INJECTING ANON-CONDENSIBLE GAS INTO SAID STRATUM ADJACENT SAID ZONE SO AS TOOBSTRUCT THE PASSAGE OF STEAM INTO SAID ZONE; AND (4) RECOVERING OILFROM SAID AT LEAST ONE PRODUCTION WELL.